In vitro Protein Synthesis by Plastids of Phaseolus vulgaris. III. Formation of Lamellar and Soluble Chloroplast Protein.

Chloroplasts from leaves of plants which had been grown in the dark, and then illuminated for 12 hours were isolated, and allowed to incorporate (14)C-leucine into protein, and the products of this incorporation were studied. Lamellar and soluble proteins are the principal products, and are formed in about equal amounts. Only some of the soluble proteins become heavily labeled. Those with highest specific activity have a molecular weight of the order of 140,000, while the higher molecular weight Fraction I protein has a much lower specific activity. The soluble protein as a whole does not serve as a precursor for the lamellar protein, and vice-versa, although a precursor-product relationship between a minor component of the soluble fraction and the lamellar fraction has not been ruled out. The relative protein synthesizing capabilities of chloroplasts and mitochondria are discussed with reference to the data presented.